“It’s very unlikely we’ll be involved in anything as successful again,” said “Downton Abbey” creator Julian Fellowes of his long-running serial, which over the course of five seasons has become the most-nominated international show in the history of the Emmys, and such a pop-culture staple that it serves as a punchline in Judd Apatow‘s “Trainwreck.”

In the middle of writing the final episode of “Downton’s” sixth and final season, Fellowes, who has written every episode of the series, reflected on the remarkable journey he’s taken with his chronicle of an aristocratic British family and their array of servants in the 1910s and ’20s.

Steve Pond: What made you decide to end the show after six seasons?Julian Fellowes: Actually, we originally thought five would be it. And it was only as we were getting started on [season] five that we realized that we didn’t really have enough time to wind everything up. And so that’s what we’ve done with six. But we were never tempted to do more.

Obviously, we’ve had lots of letters saying, “Please don’t,” which is flattering. And that is precisely why we’re ending it now, because we still get letters asking us not to. As opposed to, “Here’s your hat, what’s your hurry?”

The idea of trying to adjust to a changing world has obviously been a theme from the start, but it seemed particularly prevalent this past season.We have lots of it. We quite deliberately started the first series in 1912, because if it did run to three seasons, which was by no means guaranteed, it meant that the first three would be completely different from each other.

The first would be before the war, essentially at the end of Edwardian England, and then the second would be the war, and the third would be after the war, when the world really was different.

I mean, the 10 years between 1912 and 1922 was rather like the ’60s. The difference between 1959 and 1970 was absolutely extraordinary, and the same can be said of that time. One of the reasons we chose Highclere [Castle, the series’ main setting] is that Highclere is the most tremendous statement of aristocratic superiority. It really is a very early statement of the fact that as long as England is in the hands of the aristocracy, it’s a safe place to be.

And we chose that very deliberately for its irony as a backdrop for the decline of the power of the aristocracy and their essential retreat into a different way of life.

But you have no interest in taking the show into the ’30s.I feel the ’30s have been very much explored dramatically, and I didn’t really want to get into the whole business of the Nazis, which I think has been explored exhaustively. And I don’t know that there is anything else to be said about the Nazis.

I mean, Bob Altman and I set “Gosford Park” in November 1932, because we felt that was the last time when you could do something about the British upper classes without the Nazis. Because in January 1933 they burnt down the Reichstag, and that was the moment when a lot of people sat up and saw that this ridiculous little party of extremist nonsense people was suddenly becoming a real politically force.

The difficulty of dramatizing the Nazis, to me, is that I like ambivalent dramas, where you don’t know whose side you’re on, or maybe you change sides. You might initially think, Oh no, [Maggie Smith’s character] Violet is completely wrong in this, but as the argument goes on and as you hear more of her point of view, you understand where she’s coming from. That’s what I like.

But the Nazis don’t give you that. Nobody’s slightly on the side of the Nazis. It’s so absolute – there’s just bad guys and good guys. And there have been wonderful films about them, but I don’t think I’m the right guy to write them.

What were your priorities going into this past season?Well, Season 4 was about Mary’s redemption. That series was really about personal choice, about watching Mary decide to come alive again after her husband’s death. Series 5, you’re right, was much more to do with the fact that change was going to overtake them. And in Series 6, I would say, the theme is resolution.

Now, you can have different degrees of conclusion. In some stories, something can happen, that’s the end of the story and everyone’s either happy or unhappy. In other stories, you can suggest that in the afterlife of these characters, when they are only in the ether, this will work and this probably won’t.

I don’t think everything has to be tied up, but I think there are main themes that have to be tied up. I mean, I want you to finish the last episode feeling contented, and not feeling cheated. Sometimes in a movie the clever twist at the end just leaves you feeling cheated, and I don’t want that.

PBS

So many notable TV series have ended over the past couple of years. Did you pay attention to how “Breaking Bad” did it, or “Mad Men?”
Oh, don’t tell me! I’ve still got the second half of the last series of “Mad Men” to watch. I don’t watch it episodically on television. I wait and buy the box set, and then I’m in control. So I don’t want to hear anything about it, because I absolutely adored “Mad Men,” and I’m terribly sorry it’s over. I thought it was a brilliant, brilliant piece of television.

I never got into “Breaking Bad,” although I know it’s very good because a great many of my friends admired it a lot. I think my problem was I didn’t really like any of them. And although it sounds rather sort of petty bourgeois, I do feel I need to like someone. I don’t have to like everyone, but I feel I have to like someone.

What I thought was brilliant about Jon Hamm‘s performance is that with Don Draper, you sort of disapproved of him in every way, but there was something sympathetic in his predicament.

There are certainly characters in “Downton” whose behavior we don’t like — I mean, Lady Mary is insufferable at times, but we somehow feel for her.I think Michelle [Dockery]’s got that. She’s sort of haughty and snobbish and all that stuff, but there’s something about her that you can’t dismiss. And in the big things, Mary tends to come through. She’s only silly in the small things, where her power is being tested or something.

It is a classic showbiz role. Joan Crawford built her career on people who were essentially unsympathetic, but you were still rooting for her. So did Bette Davis.

When you get to this point on a long-running show, do you ever think, Oh, it would have been nice if we’d been able to do this…Sometimes you think of a story line and you think, Oh, we could have done that, that would have been good for us. But you know, I’m about to go into “The Gilded Age” [an NBC series set in New York in the 1880s]. I’ll do it there.

Is it emotional to know this is the last “Downton” script you’ll ever write?
Yes. I think it is, a bit. I mean to go on the set either at the end or toward the end, and I’m sure that will be emotional. And we’ll probably have a wrap party and we’ll all be in sobs, you know.

I mean, “Downton’s” been an extraordinary adventure for me. I’ve had other adventures — “Gosford” took me out of the back of the cellar and put me among the players. I had a big hit on Broadway with “Mary Poppins,” and I’ve had two best-sellers in England and America with my novels. So I think I’ve had more than my share of success, and “Downton,” in a sense, has topped them all by being this incredible phenomenon. And I feel very, very grateful.